Ohio Senator Rob Portman on Friday announced he's had a change of heart on gay marriage.

In 2004, Portman, a Republican, voted in favor of a constitutional amendment banning such unions. And in 1999 he supported a bill which sought to ban gay and lesbian couples in the District of Columbia from adopting children.

In an op-ed published in the Columbus Dispatch, Portman wrote: “I believe all of our sons and daughters ought to have the same opportunity to experience the joy and stability of marriage.”

In the piece, Portman concedes that he once felt differently.

“Then something happened that led me to think through my position in a much deeper way.”

“Two years ago, my son Will, then a college freshman, told my wife, Jane, and me that he is gay. He said he'd known for some time, and that his sexual orientation wasn't something he chose; it was simply a part of who he is. Jane and I were proud of him for his honesty and courage.”

“At the time, my position on marriage for same-sex couples was rooted in my faith tradition that marriage is a sacred bond between a man and a woman. Knowing that my son is gay prompted me to consider the issue from another perspective: that of a dad who wants all three of his kids to lead happy, meaningful lives with the people they love, a blessing Jane and I have shared for 26 years.”

Portman added that allowing gay couples to marry “doesn't amount to a threat but rather a tribute to marriage, and a potential source of renewed strength for the institution.”

However, Portman did not call for the Supreme Court to strike down Proposition 8, California's voter-approved amendment defining marriage as a heterosexual union, or the Defense of Marriage Act (DOMA). Instead, he said “change should come about through the democratic process in the states.”

“Judicial intervention from Washington would circumvent that process as it's moving in the direction of recognizing marriage for same-sex couples. An expansive court ruling would run the risk of deepening divisions rather than resolving them.”

Marc Solomon, national campaign director for Freedom to Marry, applauded Portman's new stance.

“We greatly appreciate Senator Portman's sharing his journey on the freedom to marry with his constituents and with the American people,” Solomon said in a statement. “It's a beautifully human experience for a father to listen with an open heart to his son, to reflect on his own beliefs, and conclude that he wants for his son the same opportunity for happiness that comes with being able to marry that he and his wife have.”